Ground plane antenna



Nov. 7, 1950 J. GOLDSMITH GROUND PLANE ANTENNA Filed March 10, 1947 INVENTOR. @170150/2 M d/ in their impedance characteristics.

Patented Nov. 7, 1950 GROUND PLANE ANTENNA Joseph Goldsmith, Lyons, Ill., assignor to American Phenolic Corporation, Chicago, 111., a corporation of Illinois Application March 10, 1947, Serial No. 733,625

10 Claims.

The present invention relates to radio antennas and is particularly directed to the provision of a broad banded V. H. F. (very high frequency) ground plane antenna. The invention is characterized by a novel physical structure of the antenna wherein the formation, combination, and arrangement of the individual parts result in a unitary device having an inherent impedance matching value corresponding with the characteristic impedance of a standard 52-ohm coaxial transmission line, so that maximum radiation may be accomplished and the standing wave ratio in the transmission line held to a minimum value over the entire wave band.

The efiiciency of any coupling method for maximum energy transfer depends largely upon establishing matched impedances between the two coupled circuits, since the standing wave ratio is determined by the load impedance and by the characteristic impedance of the line. In most modern installations of V. H. F. equipment, which operate in the range of 30 to 300 megacycles, the antenna is fed by a coaxial transmission line, ordinarily one of the several standard sizes of lines commercially manufactured. The different types of antennas in use, however, vary widely Thus, While it is well known in the art that maximum power transfer can be accomplished onl in a circuit in which the impedance of the antenna is correctly matched to that of the transmission line, the ideal condition rarely exists in practice. This is especially true in a broad banded antenna where the band of operation must extend over a range of frequencies.

In view of this, it has been the practice in the art to select an antenna design arbitrarily and to then attempt to match the antenna to the transmission line by the use of some sort of matching, section, as by the provision of a reactive component in the circuit. It has long been recognized that either resistances or reactances may be utilized and that they maybe placed in seriesor in parallel with the line, as required. The factors most important in determining the choice of matching devices have often been outlined in the technical literature of the art, which includes extended discussions of the general principles involved in matching various types of an-. tennas and lines b single inductances and capacitances, as well as by various networks. dinarily the matching procedure requires elaborate testing of the antenna and measurement of its impedance at different frequencies so that these may be graphed and analyzed as a pre-v liminary step to selecting the proper type of reactive element and estimating the value required, followed by repeated tests with different rea tances until a reasonably good match is obtained.

It is accordingly submitted by the present applicant that even when theoretically perfect match is obtained, this method of solution of the problems of antenna matching falls far short of offering a universally workable solution to the practical problems involved. For one thing, it offers no direct answer to the problems, but only serves as a guide in an extended cut and try process requiring repeated experiments, measurements, and tests. Also, such methods fail to solve the practical difficulties of simultaneously matching the load and line and yet providing adequate physical strength for the antenna, ade-' quate physical support for the line, affording proper insulation, providing a factor of safety to prevent damage to equipment or personnel due to lightning or accidental high-voltage charges, and overcoming troublesome problems of maintenance.

It is therefore the prime object of the present invention to provide a broad banded antenna having its physical parts so designed and related that the antenna is inherently matched to a standard 52-ohm transmission line, so that maximum power transfer may be accomplished without the necessity of resorting to coils, condensers, or matching sections. The antenna here disclosed has good broad band characteristics, and thorough tests show it to match a 52-ohm line so well as to show a standing wave ratio of less than 1.5 to 1 over the entire band. Such an antenna not only eliminates the need for out and try methods of matching, but has the further advantage that it avoids the use of coils, condensers, etc., in the immediate vicinity of the antenna mounting andrconsequently avoids the difiiculties of properly housing and insulating these elements. Its size and shape are directly determinable from a frequency or wavelength within the band in which it is designedto operate, so that no experimentations, tests, or measurements are required. In'addition, it simplifies the construction of all exposed parts of the'circuit sothat the problems of maintenance and possibilities of antenna failure are reduced. 7

A further object of the invention resides in the provision of an antenna having a. physical structure inherently matched to the impedance of a standard 52-ohm transmission line whereinthe transmission line is joined to theantenna in'a simple and efiicient manner so that all of the parts are firmly joined to each other and the entire structure is unusually sturdy and capable of withstanding the most rugged service. It is well suited to railroad or other rough use, since it withstands shock, vibration, and weather. The entire antenna structure functions as a unitary piece of solid metal and is fully grounded. It operates at ground potential as to A. C. and D. C. charges. In use, it is entirely safe and may be located on a railroad car, for example, .1

in a position where members of the train crew might accidentally touch it without fear of injuries. Also, the fact that it is at ground potential means that there is no danger of injury to persons handling the radio equipment in the event the antenna should accidentally be fouled by power lines or struck by lightning. These features not only provide an antenna that is perfectly safe and unusually strong, but also eliminate the need for any insulation other than that required in the termination of the transmission line, so that problems of electrical leakage or breakdown are alleviated without sacrifice of dependability or efficiency of performance.

The foregoing objects are accomplished in the teachings of this invention by the provision of an antenna structure of extremely rugged, all metal construction, wherein all of the several parts are firmly joined to each other and are in intimate electrical union. The entire antenna unit may be conveniently grounded by securin the base to the steel top of a locomotive cab, if wsed on a railroad installation, or by placing it on a ground skirt or ground plane. Thus the specific design disclosed here has the physical requirements of a good antenna as well as the necessary electrical characteristics to achieve a proper match between the line and the load, and since these objects are accomplished without complications in the physical structure of either line or load, it may well be said that the invention per: mits a perfect reconciliation of the essential physical and electrical properties.

Referring now to the drawings attached to and forming a part of the present specifications:

Figure 1 is a detail central sectional View of an antenna constructed in accordance with the teachings of this invention, showing an installation in which the radiator is mounted on a ground plane comprising a fiat metal sheet.

Figure 2 is a perspective view of the antenna, with a pole top mounting including a circular skirt to act as a ground plane.

'The antenna may be mounted on any surface, such as indicated by the ordinal I0. If this is a metal or other conducting surface of substantial area, it will serve as the ground plane, but if the surface In is of non-conducting material, a separate sheet II of metal is used. In the latter and extends downwardly from the head to a point adjacent to the base I2. Since the inside diameter of the sleeve is of considerably greater diameter than the supporting shaft, the inner walls of the sleeve are spaced apart from the outside surfaces of the shaft. Also, the sleeve terminates short of the base I2 so that it is electrically separate from it.

Since it is contemplated that the antenna will be fed by a coaxial transmission line, a bracket 2| is afiixed to the base I2 to provide a sturdy mounting and good grounding connection for the termination 22 of the coaxial line. The outside conductor of the line is electrically joined to the bracket 2I and consequently grounded to the base l2 and ground plane I I, and the central conductor of the line is joined to the sleeve I9 by a flexible lead 23. The lead should be connected on the outside and at the lower end of the sleeve, as by the screw 24.

In certain instances it may be desirable to use the antenna on a post mounting or other support where the provision of a fiat plate I I is impractical, and in such an instance the base I2 may be mounted directly on the hub 25 of a circular skirt 26 at the top of the supporting pole 21 (Figure 2) The base I2 of the antenna is drilled so that the termination fitting 28 of the coaxial feed line 29 may extend upwardly through the base and be connected to the lower end of the sleeve as in the previous case.

From the foregoing, it will be apparent that the teachings of this invention provide an unusually strong and rugged physical structure for a radio antenna with the several parts of the structure simple in form, strong, easy to assemble, and well adapted to modern mass production methods of manufacture. Moreover,the antenna is of metal, so that problems of electrical insulation are largely avoided and the possibilities of breakage or accidental damage further reduced. In addition, the antenna is intimately connected with the ground plane plate, so that all parts of the antenna structure are adequately grounded and thus cannot carry high potential charges. This will safeguard the radio apparatus and the person of the operator in the.

event that the antenna should be struck by lightning or accidentally come in contact with high tension power lines.

case, it has been found satisfactory to provide a plate sufliciently large so that the distance R is somewhat greater than the height of the antenna and represents a radius of at least onequarter wave length.

The antenna structure includes a circular base plate l2 drilled to receive bolts or cap screws I3 which anchor the antenna assembly in position. The base I2 also has a central opening I4 in which a vertical supporting shaft I5 is fitted. The shaft I5 extends upwardly into a socket I6 in a cylindrical-head I1, so that the shaft serves to support the head. The upper end of the head is preferably round, as indicated'at I8. A tubular sleeve IQ of the same outside diameter as the head I! is mounted on the lower end of the head It has previously been pointed out that the problems incident to the practical design of a commercially acceptable antenna. structure involve not only a decision as to' the general structural features but also call for a determination of the exact proportions and dimensions adapted to give the best results in any given frequency band. The dimensional relationship of the parts may. be quite critical, since it is not only necessary that the antenna be properly dimensioned to radiate a given frequency, but it is also essen' tial 'that the impedance value looking into the antenna must remain sufiiciently constant so that it matches the impedance of the transmission line over a wide range of frequencies. 1

It has been learned that while the general of the supporting shaft is equal to .12 of the wave length; and the outside diameter of the supwhere lambda indicates the wave length and f and 1) indicate the frequency and velocity, respectively. Since the velocity of the wave may be expressed as 3 meters per second, values may be substituted so that the formula develops to be:

Converting from metric units to inches:

=l.875 meters. (Approx) then lambda .19=l4.02 inches lambda .12=8.86 inches lambda .0,10=.74 inches lambda .024=1.772 inches lambda .025=1.846 inches These dimensions may be departed from suff1- ciently so that convenient fractional dimensions may be substituted for the exact decimal dimensions indicated, and it follows that materials of standard sizes available on the commercial market may be used to construct the unit. In commercial practice the height might be specified as between 14 and 14% inches, the shaft height about 9 inches, with a %-inch rod used for the supporting shaft, a l%-inch diameter rod for the head, and tubing of 1% O. D. and l%-inch I. D. for the sleeve. The same dimensional formula may be used to determine the critical dimensions required for higher or lower frequencies.

It is unnecessary to utilize the out and try method heretofore practiced in the art, and acceptable matching can be obtained by utilizing a standard 52-ohm transmission line without the necessity of conducting tests to determine the impedance of the antenna or altering the antenna structure to provide for the insertion of coils or condensers between the end of the line and the radiating element of the antenna. Moreover, these results are obtained without the need of resorting to intricate circuits or complicated structures. Most important, they are the product of the inherent characteristics of the antenna disclosed and do not depend on the accuracy of measurement of the impedance of the load after the antenna has been constructed, nor on the proper calculation of the nature and 'value of the reactance necessary to bring about the correct match. It follows that by utilizing these teachings, it is entirely feasible to depart from the conventional cut and try method of matching and that the present invention provides an easy and satisfactory solution for a problem that has long baiiied experts working in this field.

The invention not only eliminates the need of condensers or coils between the feed line and the antenna and by so doing eliminates the problems normally encountered in attempting to insulate and house these reactances but, in addition, permits a direct solution of the antenna problem. It is unnecessary to experiment with the form and dimensions required since these are determinable by direct calculation from any frequency within the band in which the antenna is to be used. Some variation of dimensions and proportions is permissible, and while the degree of variation to be permitted cannot be arbitrarily set, it is considered excellent performance to keep the standing wave ratio below 1.5 to l, and variations within these limits are acceptable. It is unnecessary to make measurements of the antenna impedance to construct the antenna for a given frequency, however, and it naturally follows that these teachings can be successfully followed even when no test equipment is available so that prior methods of matching would be out of the question. Moreover, the invention accomplishes these results by the utilization of an unusually simple mechanical construction wherein all of the exposed parts are heavy and rugged in nature, Well able to Withstand long use, and not apt to be damaged by ordinary abuse.

The exact form of the invention illustrated in the drawings and described herein is the present preferred embodiment of these teachings and is chosen as the best example by which its characteristics can be described. It is known, however, that certain changes may be made in al-' most any electronic apparatus, particularly if compensating features are added, and it is ac cordingly contemplated that considerable departure from the exact form and proportions shown may be made without sacrifice of all of the advantages inherent in the invention. It is accordingly pointed out that the scope of the inventive thought extends well beyond the specific structure shown, and it includes any variations or modifications coming Within the terms of the appended claims.

Having thus described my invention, What I claim as new and desire to patent by United States Letters Patent is:

1. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with a head portion at the upper end of the shaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft to a point adjacent the base, wherein the height of the radiator is .19 of the wave length, the height of the shaft .12 of the wave length, and the diameter of the supporting shaft and internal and external diameters of the sleeve are substantially .010, .024, and .025 wave length, respectively; so that the impedance looking into the antenna matches the characteristic impedance of a 52-ohm transmission line to provide a standing wave ratio of less than 1.5 to 1 in the line.

2. In a broad band antenna for the very high frequency range including at least one radiating element, the improvement that resides in the provision of a radiator consisting of a base and a supporting shaft with a head portion at the end of the supporting shaft; a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously from the head of the shaft to a point adjacent the base, wherein the length of the radiator is .19 of the wave length, the length of the shaft .12 of the wave length, and the diameter of the supporting shaft and internal and external diameters of the sleeve are substantially .010, .024, and .025 wave length,

respectively.

- 3. In a broad band antenna for the very high frequency range-including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head at the upper end of the shaft and a single hollow tubular-sleeve surrounding and. spaced fromthe' supporting shaft and'electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft to a point adjacent the base, wherein the height of the radiator is .19 of the wave length, and its external diameter is substantially .025 wave length.

4. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head atthe uper end of the shaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft to a point adjacent the base, wherein the height of the radiator is .19 of the wave length, the height of the shaft .12 of the wave length, and the external diameter of the sleeve is substantially ,025 wave length, so that the impedance looking into the antenna matches the characteristic impedance of a 52 ohm transmission line. a j,

I 5. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, theimprovement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head at the upper end of theshaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft substantially the length of the shaft but electrically separate from the base,

wherein the height of the radiator is less than a quarter wave length, the height of the shaft is over'half the height of the radiator, and the ratio of the height of the radiator to its diameter is no greater than eight to one, so that the impedance looking into the antenna matches the characteristic impedance of a 52 ohm transmission line to provide a standing wave ratio of less than;1.5 to l in the line.

6. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head at the'upper end of the shaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the shaftsubstantially the length of the shaft but electrically separate from the base.

'7. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head at the upper end of the shaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft substantially the length of the shaft but electrically separate from the base, wherein the base, supporting shaft, head, and sleeve are all of metallic conducting material and in intimate electrical contact with each other so that the antenna constitutes a sturdy, compact, all metal structure.

8. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the combination, with a coaxial transmission line, of a radiator consisting of a base and vertical supporting shaft with an enlarged cylindrical head at the upper end of the shaft and a single hollow tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its length below the head and extending continuously downwardly from the head of the shaft substantially the length of the shaft butelectrically separate from the base, wherein the outer conductor of the coaxial transmission line is connected to thebase and the central conductor of the line is connected to the lower end of the sleeve; and wherein the base, supporting shaft, head and sleeve are all of-metallic conducting material and in intimate electrical contact with each other and with the ground plane, so that the antenna constitutes a sturdy, compact, all metal structure adapted to operate at ground potential.

9. -In a broad band antenna for the very high frequency rangeincluding a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator having capacity loading in the upper portion thereof to shorten the required physical length of the radiator, said radiator including a vertical supporting shaft with an enlarged cylindrical head at the upper end of the shaft and a single, hollow, tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its entire length below the head, saidsleeve extending continuously downwardly from the'head of the shaft substantially the'length of the shaft but electricallyv separate from the base wherein the height of the radiator is less than one-fifth of its resonant wave length. 4

10. In a broad band antenna for the very high frequency range including a ground plane and a vertically polarized radiator on the ground plane, the improvement that resides in the provision of a radiator having capacity loading in the upper portion thereof to shorten the required physical length of the radiator, said radiator including a vertical supporting shaft with a head portion at the upper end of the shaft and a single, hollow, tubular sleeve surrounding and spaced from the supporting shaft and electrically separate therefrom throughout its entire length below the head, said sleeve extending continuously downwardly from the head of the shaft substantially the length of the shaft but electrically separate from the base wherein the length of the sleeve below the head is less than 0ne-eighth of the resonant Wave length of the antenna.

JOSEPH GOLDSMITH.

REFERENCES CITED The following references are of record in the file of this patent:

Number OTHER REFERENCES Electronics, March 1947, page 46. 

